A General Packet Radio Service (GPRS) Tunnelling Protocol (GTP) is a well-known protocol used for setting up GTP tunnels between nodes for separating traffic into different communication flows.
As is well known, in GTP Version 1 (GTPv1), GTP tunnels are e.g. set up over the Gn interface between GPRS Support Nodes (GSNs) such as Serving GPRS Support Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs) within a Public Land Mobile Network (PLMN), and over the Gp interface between GSNs in different PLMNs.
In GTP Version2 (GTPv2), which modifies and enhances GTPv1 used in 2G and 3G mobile networks and is commonly referred to as evolved GTP (eGTP) for use in an Evolved Packet Core (EPC) network in a Long-Term Evolution (LTE) system, GTP tunnels are set up between various interface, such as the S5/S8 interface between a Serving Gateway (SGW) and a Packet Data Network Gateway (PGW), the Sn interface between a Mobility Management Entity (MME) and an SGW, the S2b interface between an Evolved Packet Data Gateway (ePDG) and a PGW, etc.
A GTP message consists of a header followed by zero or more information elements (IEs). The header defines, for instance, GTP version, total length of message and tunnel endpoint identifier. In GTPv2, 256 different IE types exist, each IE type being identified by an IE type value from 0 to 255.
The IE type value defines a great variety of message characteristics exemplified e.g. by Mobile Equipment Identity (MEI)—value 75, User Location Information (ULI)—value 86, Bearer Context—value 93, Packet Flow Id—value 123, etc., see for instance technical specification 3GPP TS 29.274 V13.2.0.
Recently, in order to implement new features of the 3rd Generation Partnership Project (3GPP) in the GTPv1 and GTPv2 protocol, a large number of new IE types are specified, leading to less and less (possibly less than 20 in GTPv1 and possibly less than 50 in GTPv2) new IE types left as spare IEs. This may endanger efficient support of more features in the GTPv2 protocol in the future.